This section is intended to introduce the reader to various aspects of art, which are related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
On a local loop, where a telephone exchange is connected to a phone located on customer premises, the analogue voice services, or plain old telephone service, noted POTS, typically use the 300 Hz to 3400 Hz frequency range. The local loop is also called the unshielded twisted pair (UTP) telephone line. The Digital Subscriber Line technology, noted DSL, uses the frequencies above the POTS range permitting to share the copper wire that was originally intended only for the public switched telephone network, noted PSTN. Typical DSL over PSTN deployments require a DSL modem to communicate with the digital subscriber line access multiplexer, noted DSLAM, located in the public switched telephone network (PSTN) telephone operator's central office (CO) and the analogue phones to be plugged to the residential phone wire through a low-pass filter. As such the analogue phone is coupled to the phone service central office, or foreign exchange station, noted FXS, and the DSL modem is coupled to the DSLAM. Hence, on the same local loop, two channels coexist: the analogue phone channel and the DSL channel.
DSL technology permits the customer premises to access the Internet through the Internet Protocol, noted IP. A DSL gateway located in the customer premises comprises a LAN interface via which devices connect to the Internet. LAN Devices may run different kinds of applications amongst which voice over IP, noted VoIP. VoIP is performed with applications running on personal computers or running embedded on gateways with either dedicated VoIP terminals connected to the LAN or regular analogue telephones connected to dedicated VoIP hardware. The LAN may be a wired network such as an Ethernet network or a wireless network such as a WiFi network. The dedicated VoIP hardware is a combination of a local foreign exchange office, noted FXO, and a local set of foreign exchange stations (FXS). The FXO is an interface that receives the PSTN service from the FXS located in the CO. It generates among others the on-hook and off-hook event indicators. The local FXSes allow the connection of an analogue phone, permitting local telephones to be connected transparently over IP to the FXS located in the CO in order to access the same PSTN services as telephones that are directly connected, via the residential phone wiring, to the PSTN. The VoIP service is not using the public switched telephone network; it is running over IP via the Internet.
Gateways supporting a VoIP service, allow two parallel paths to the PSTN. This concept enabled the removal of the PSTN CO. In such a scenario, the operator reduces operational costs and the customer premises will keep the PSTN service via VoIP. When the customer premises are no longer connected to the PSTN CO, the phones plugged to the residential phone wire can no longer access the POTS services. A DSL gateway that comprises subscriber line interface means still permits the phone plugged to the FXS interface to perform voice service with VoIP. The European Patent Application EP1827055 discloses a method, at the gateway, enabling the phones linked to the residential phone wire to perform voice services with VoIP without having to modify the residential phone wiring. This method is called re-injection hereinafter. The requirement is that the old PSTN CO is being removed from the line because the FXS port (once reinjected) takes over its function.
The FIG. 14 represents the system of EP1827055. A local loop 3 connects the customer premises 1.1 to a central office 30 to which the customer premises are connected. The central office 30 comprises a digital subscriber line access multiplexer 25, noted DSLAM, and a PSTN central office 31. The DSLAM intends to couple to the DSL gateway 1 located in the customer premise; which means that the DSL gateway registers to the DSLAM and is associated with the DSLAM in a point to point connection. It offers DSL services to the DSL gateway. It permits the customer to access the Internet 20. The PSTN central office 31 comprises a foreign exchange station 32, noted FXS. The FXS is connected to the local loop via a low pass filter 33; which is required because of the presence of the DSL connection on the local loop. This prevents the higher tones of the DSL from disturbing the working of the analogue PSTN service. The phone 7 is coupled to the PSTN CO 31, it receives the PSTN services via the FXS 32. The FXS comprises a phone subscriber line interface circuit, noted SLIC, not represented on the figure. The SLIC performs the BORSCHT functions; BORSCHT standing for battery, overvoltage, protection, ringing, supervision, codec, hybrid, and testing. The SLIC might be discretely implemented onto a line card or in an integrated circuit. The customer premises comprises an interface between the local loop and the residential phone wire, the minimum point of entry 5, noted MPOE. The residential phone wire 110 contains several plugs, 1100, 1101, in order to connect a PSTN device or a DSL device such as a DSL gateway or a DSL modem. The plug is for example a standard connector, noted RJ-11, and might be any other kind of electrical connector intended for telephony or data. The PSTN devices connected to the plug may be a wired phone, a cordless phone, a fax or a voiceband modem. A base station such as a DECT base station attached to the plug permits to connect several DECT terminals. Hereafter in the document, the phone represents all the devices intended to transmit and receive voice frequency signals. It includes for example the phone, a DECT system including the base station, the cordless phone, a fax and a voiceband modem. The DSL gateway is connected to the customer premises through the DSL interface. A phone 7 is also connected to the residential phone wire through a low pass filter 6. The DSL gateway 1 comprises a LAN interface in order to provide the access to the Internet 20 to all the devices, such as a PC 9, connected to the LAN 10. The DSL gateway comprises an interface for connection to a phone 8. The interface is an FXS interface. The phone may access the PSTN service provided by the FXS located in the PSTN central office 31. The phone 8 may also access the voice services provided by the gateway; the phone 8 is then not coupled to the FXS located in the central office 30, it is coupled to the FXS located in the gateway 1. The gateway then performs VoIP through the DSL connection.
Traditionally, the PSTN telephone operator owns his telephone line wiring from the CO to the end-customer premises. In practice this means that subscribers can only subscribe to a DSL service if they already have a PSTN subscription with a telephone number. Telecom operators may provide VoIP services without owning PSTN infrastructure. Each customer receives one or more telephone numbers so that he/she is able to initiate or receive voice calls. For regulatory reasons, PSTN providers are obliged to unbundle the local loop to stimulate competition and allow other telecom companies to have nondiscriminatory access to this part of the telecommunication network.
For customers that have a PSTN voice subscription and telephone number, the unbundling process may impact their voice service: the PSTN phone number is no longer valid and they need to switch to a VoIP subscription using a different phone number. While operators are regulatory obliged to perform loop unbundling, they want to minimize the impact on end-users and ensure continuity of the voice server, ideally without a change of telephone number from PSTN to VoIP.